The energy consumption in an electrical vehicle is a very important issue because batteries that are hitherto used do not provide an autonomy that is equivalent to the gas-powered vehicles. The main source of power of an electrical vehicle is generally the batteries. Such batteries are usually provided in a large number and are distributed in various locations throughout the vehicle. A major development in the field of batteries may some day allow the use of a reduced number of batteries, or perhaps a single battery, that would considerably make the vehicle lighter and with an enhanced autonomy. Meanwhile, the issue of energy consumption is still very significative for the automobile industry.
An electrical vehicle comprises an electrical traction motor that is connected to a front or rear wheel of the vehicle by means of a main axle. Depending on the design of the vehicle, the traction motor may power more than one wheel, either front or rear wheels. Some vehicles may also have a traction motor on each wheel. Very compact designs have even allowed the possibility of providing the traction motor as a motor wheel, where the motor is embedded within the rim of a wheel without any gear box.
Hybrid vehicles are also electrical vehicles by extension. Some hybrid vehicles use an auxiliary engine driving a generator to charge to main batteries. The driven generator provides additional power during specific conditions, such as high speed or loads. Other hybrid vehicles use a conventional engine with direct mechanical connection to the wheels for high speed and the electrical traction motor or motors for urban travelling or during a dense traffic. The conventional engine is switched off and disconnected from the wheels when the electrical traction motor or motors are used.
The traction motor or motors are usually not the only systems that use power since an electrical vehicle comprises many other electrical equipments or mechanically-driven devices, depending on the options. Examples of electrical equipments are the electric or electronic controls, the blower fan, the wiper motor, the interior and exterior lights, the powered windows or door locks, the defroster, etc. Typical examples of mechanically-driven devices are a power steering pump for a power steering system or a compressor for an air conditioning unit. The power steering pump is a major problem on the electrical vehicles.
In general, the electrical equipments are connected to a "low" voltage DC circuit, of 12 or 24 volts for instance, itself connected to an auxiliary battery of the vehicle. The main batteries supply power at a relatively "high" voltage for driving the traction motor or motors. The high voltage is about 72 to 144 Volts DC for instance. It may be higher for specific applications. The low voltage DC circuit is usually powered by the main batteries with the use of a DC-DC converter and an auxiliary low voltage battery. A very common problem with DC-DC convertor is that the output low tension tends to fluctuate as the input high tension changes. For instance, the voltage of the main batteries drops whenever the vehicle accelerates. The fluctuation is often felt in the electrical equipments connected to the low voltage DC circuit, as for instance, the intensity of the lights changes or the speed of the wiper motor varies. These fluctuations are very disturbing over time for both the driver and the passengers. One way to resolve the problem is to use a highly efficient DC-DC convertor. However, the high cost of such convertors is a major inconvenient.
The mechanically-driven devices in an electrical vehicle, which generally comprise a power steering pump, are driven by an auxiliary motor. The auxiliary motor usually runs continuously whenever a corresponding device needs to be driven, regardless of the speed of the vehicle. As a result, the traction motor or motors and the auxiliary motor are often driven simultaneously when the vehicle is in motion. Some electrical energy is thus wasted, partly because the auxiliary motor is not perfectly efficient and is usually less efficient than a traction motor. Moreover, the operation of the auxiliary motor in addition to the traction motor or motors adds unnecessary noise.